This application claims priority of Korean Application No. 2001-15953, filed on Mar. 27, 2001 in the Korean Patent Office, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a projection display system and, more particularly, to a screen with an improved viewing angle characteristic and a projection display system for realizing a projection image using the screen.
Projection display systems, such as projection televisions and video projectors, have an image display device, such as a specially manufactured small-sized cathode ray tube (CRT), a liquid crystal display (LCD), or a polymer dispersed liquid crystal (PDLC), for generating the image. The generated image is enlarged and projected to a large-sized screen by a projection lens so that the final image transmitted to a user can be easily seen. Projection display systems which provide such enlarged images to the user are increasingly becoming in great demand.
Such a projection display system includes a light source for generating white light, a shutter for allowing light to come through in response to an image signal, a lens for enlarging and projecting the image light coming through the shutter, and a screen on which the image light that is enlarged and projected by the projection lens is displayed.
The screen includes a Fresnel lens for converting the image light from the projection lens into parallel light so as to display the image with a uniform brightness throughout the whole area of the screen, a Lenticular lens for diffusing the parallel light from the Fresnel lens, and a protecting panel for protecting the Lenticular lens.
A light-incoming surface of the Lenticular lens is provided with plural cylindrical convex lenses, and a light-outgoing surface of the Lenticular lens is provided with plural convex lenses and a light absorption layer.
However, to satisfactorily provide good display quality to a plurality of users watching the screen of the projection display system, particularly when the users are widely dispersed in the horizontal direction with respect to the screen, the screen must provide a wide viewing angle in the horizontal direction.
To widen the viewing angle of the screen in the horizontal direction, U.S. Pat. No. 6,130,777 discloses a projection screen having a Lenticular lens sheet provided at its light-outgoing surface with a plastic film having orderly arranged minute ridges.
In addition, U.S. Pat. No. 6,097,539 discloses a projection screen having a Lenticular lens provided at its light-outgoing surface with two asymmetric total reflecting lenses arranged in the lengthwise direction.
In recent years, a three-dimensional projection display system has been developed. U.S. Pat. No. 5,703,606 discloses such a three-dimensional projection display system realizing the three-dimensional image by rotating the screen at a predetermined speed. For the user to watch the three-dimensional image, the screen should provide the viewing angle of about 180xc2x0 in horizontal and vertical directions of the screen.
However, the above-described screens for the projection display systems are not designed to provide a sufficient viewing angle in the vertical direction. Therefore, such screens cannot be employed in the three-dimensional projection display system.
Accordingly, to obtain a sufficient viewing angle in the vertical direction of the screen, an optical diffusing agent is added in the Lenticular lens to enlarge the viewing angle in the vertical direction of the screen. However, the light becomes excessively diffused and reflected rearward, deteriorating the contrast of the image.
Therefore, the present invention has been made in an effort to solve the above described-problems.
In accordance with the present invention, a screen for a projection display system is provided that can sufficiently provide horizontal and vertical viewing angles, thereby improving the viewing angle characteristic while maintaining a good contrast characteristic.
Further in accordance with the present invention, a projection display system using such a screen is also provided.
The screen for the projection display system includes a Fresnel lens for converting incoming light into parallel light. A Lenticular lens is disposed on a surface of the Fresnel lens to change a path of the parallel light from the Fresnel lens, providing a three-dimensional image to a user. The Lenticular lens includes a plurality of pixel lenses corresponding to pixels of the screen. Each of the pixel lenses has a central diffusing portion formed on a light-outgoing portion and a peripheral diffusing portion formed on a peripheral portion of the central diffusing portion. A sectional shape of the pixel lenses with respect to horizontal and vertical directions of the screen may be made radially symmetrical. The central diffusing portion may be formed in a hemispherical shape and the peripheral diffusing portion may be formed as a wing enclosing the central diffusing portion. A distance between a first top of the peripheral diffusing portion and a light-incoming portion of the Lenticular lens may be made greater than a distance between a second top of the central diffusing portion and the light-incoming portion of the Lenticular lens. The first top of the peripheral diffusing portion may be such that when an angle between a line normal to the first top and a path of the parallel light coming in to the first top is xcex1, the angle xcex1 becomes 45xc2x0. The pixel lenses may be formed of a material having a refractive index more than 2.
According to another aspect of the present invention, a projection display system includes a projector for generating an image and a screen for converting the image from the projector into a three-dimensional image. The screen includes a Fresnel lens for converting incoming light into parallel light and a Lenticular lens disposed on a surface of the Fresnel lens to change a path of the parallel light from the Fresnel lens and to provide a three-dimensional image to a user. The Lenticular lens includes a plurality of pixel lenses corresponding to pixels of the screen. Each of the pixel lenses includes a central diffusing portion formed on a light-outgoing portion and a peripheral diffusing portion formed on a peripheral portion of the central diffusing portion. The screen may be rotatable by a motor. The projection display system may further include an optical shutter for adjusting a light transmission rate in response to an image signal, the shutter being disposed between the Fresnel lens and the Lenticular lens. The optical shutter may be formed of an FLCD (Ferroelectric Liquid Crystal Display).